Ferromagnetism below 10 K in Mn-doped BiTe
J. W. G. Bos,1 M. Lee,2E. Morosan,1H. W. Zandbergen,3W. L. Lee,2N. P. Ong,2and R. J. Cava1 1Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
2Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
3National Centre for High Resolution Electron Microscopy, Delft Institute of Technology, Delft, The Netherlands 共Received 11 April 2006; revised manuscript received 6 July 2006; published 22 November 2006兲 Ferromagnetism is observed below 10 K in关Bi0.75Te0.125Mn0.125兴Te. This material has the BiTe structure, which is made from the stacking of two Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure analysis shows that Mn is localized in the Bi2blocks, and is accompanied by an equal amount of TeBi antisite occupancy in the Bi2Te3blocks. These TeBiantisite defects greatly enhance the Mn solubility. This is demonstrated by comparison of the关Bi1−xMnx兴Te and 关Bi1−2xTexMnx兴Te series; in the former, the solubility is limited to x = 0.067, while the latter has xmax= 0.125. The magnetism in 关Bi1−xMnx兴Te changes little with x, while that for关Bi1−2xTexMnx兴Te shows a clear variation, leading to ferromagnetism for x⬎0.067. Magnetic hysteresis and the anomalous Hall effect are observed for the ferromagnetic samples.
DOI:10.1103/PhysRevB.74.184429 PACS number共s兲: 75.50.Pp, 61.66.Fn
INTRODUCTION
The integration of ferromagnetism into semiconductors is of great current interest.1 Perhaps the best understood
ex-amples are molecular beam epitaxy共MBE兲 grown thin films of Ga1−xMnxAs and In1−xMnxAs, where a few percent Mn substitution induces ferromagnetism with maximum Curie temperatures around 170 K.2,3 In this case, Mn acts as an
acceptor, providing holes that mediate a ferromagnetic inter-action between the local moments of the open d shells in the Mn atoms. Carrier induced ferromagnetism has also been reported for Pb1−x−ySnyMnxTe,4 MBE grown p-doped Cd1−xMnxTe quantum wells,5 and Zn1−xMnxTe epilayers,6 which have much lower Curie temperatures 共below 5 K兲. Bulk samples of Cd1−xMnxTe and Zn1−xMnxTe typically show spin-glass behavior, but do show strong coupling be-tween the sp bands and localized d electrons, evidenced, for example, by the giant spin splitting of the bands or the mag-netic field induced metal-insulator transition.7This does not
lead to ferromagnetism, however, which only occurs after hole doping. In metallic systems, such as Cu1−xMnx, the ran-dom substitution of Mn in the Cu host lattice leads to spin-glass behavior.8
Here we report the synthesis and characterization of Mn doped BiTe; ferromagnetism rather than spin-glass behavior is observed. Mn and Fe doped Bi2Te3have been reported as
have V, Cr, and Mn doped Sb2Te3. For single crystals of
Sb2−xTMxTe3 ferromagnetism is reported for TM= V 共Tc = 22 K, x = 0.03兲 共Ref.9兲 and Cr 共Tc= 20 K, x = 0.06兲,10while TM= Mn 共xmax= 0.045兲 共Ref. 11兲 remains paramagnetic
down to 2 K. For Bi2−xTMxTe3, Curie temperatures of 12 K
共TM=Fe, x=0.08兲 共Ref. 12兲 and 10 K 共TM=Mn, x=0.02 and 0.04兲 共Refs.13and14兲 are reported. However, questions remain regarding the origin of the FM state in the latter two materials. For example, Bi2−xFexTe3has a maximum
magne-tization of only⬃0.025B/ Fe共x=0.08兲, and the transition
temperatures for the two reported Bi2−xMnxTe3compositions
are identical. The studies so far have reported the magnetic and transport properties of these systems but contain no structural analysis. Here, we report the first case in this
fam-ily of compounds where structural analysis proves that the Mn is incorporated within the semiconductor, and allows for its position within the lattice to be determined. The system reported is Mn-doped BiTe, which is part of the same chemi-cal family as Bi2Te3.
BiTe belongs to the共Bi2Te3兲m·共Bi2兲n homologous series, which is composed of different ratios of stacking of five-layer Te-Bi-Te-Bi-Te 共5兲 blocks and two-layer Bi-Bi 共2兲 blocks.15 For example, Bi
2Te3 has three rhombohedrally
stacked 共5兲 blocks per unit cell, and BiTe is built up from two 共5兲 and one 共2兲 blocks. Van der Waals gaps exist only between adjacent 共5兲 blocks, making Bi2Te3 and BiTe true
two-dimensional共2D兲 materials. Band structure calculations on the isostructural and isoelectronic 共Bi2Se3兲m·共Bi2兲n ho-mologous series indicate that Bi2Se3 is a narrow gap
semi-conductor, whereas Bi-Bi block containing materials are semimetals.16,17These calculations also confirm the absence
of anionic Se-Se bonding in BiSe, and suggest the assign-ments of formal oxidation states of共Bi0兲
2and共Bi3+兲2共Se2−兲3.
The addition of the zero-valent Bi2blocks therefore does not
change the charge balance in the Bi2Se3 layers and explains
the formation of the共Bi2Se3兲m·共Bi2兲nhomologous series. In the current work, structural analysis of Mn doped BiTe shows that Mn preferentially occupies sites in the Bi2blocks. The maximum Mn solubility in 关Bi1−xMnx兴Te is 0.067, which corresponds to a共2兲 block composition of Bi0.8Mn0.2.
The 关Bi1−xMnx兴Te materials exhibit Curie-Weiss paramag-netism down to 5 K. Introduction of corresponding TeBi
an-tisite occupancy in the共5兲 layer increases the solubility of Mn dramatically, and for 关Bi1−2xTexMnx兴Te the maximum solubility is 0.125. Ferromagnetism is observed below 5 K for x = 0.100 and below 10 K for x = 0.125, corresponding to 共2兲 block compositions of Bi0.7Mn0.3and Bi0.625Mn0.375,
re-spectively.
EXPERIMENTAL
Initial attempts to synthesize Mn intercalated Bi2Te3with
type phase. Detailed structural analysis共below兲 showed Mn and an equal amount of Te to occupy different Bi sites. To confirm this, a series of compounds with formulas 关Bi1−2xTexMnx兴Te and 关Bi1−xMnx兴Te 共0.033艋x艋0.167兲 was synthesized. The initial composition 共corresponding to x = 0.125 in关Bi1−2xTexMnx兴Te兲 was obtained by heating small pieces of elemental Mn 共99.95%兲, Bi 共99.99%兲, and Te 共99.99%兲 in the ratio 1:6:9 at 800 °C for one day, followed by a two week anneal 共with two intermediate regrindings兲 of homogenized pressed pellets at 575 ° C. The 关Bi1−2xTexMnx兴Te and 关Bi1−xMnx兴Te series were synthesized by heating intimately mixed Mn, Bi, and Te powders slowly to 525 ° C, followed by a two week anneal of pressed pellets at 525 ° C共with two intermediate regrindings兲. All syntheses were done in vacuum sealed quartz tubes. Phase purity was checked by powder x-ray diffraction共PXD兲 on a Bruker D8 Focus diffractometer with Cu K␣ radiation and a diffracted beam monochromator. The GSAS suite of programs was used for Rietveld fitting of the PXD data.18A pseudo-Voigt
function was used to describe the peak shape. Elemental mapping using energy dispersive x-ray共EDX兲 analysis was performed on the samples. This mapping indicated that samples that were found to be single phase by x-ray diffrac-tion displayed a homogeneous distribudiffrac-tion of Mn, Bi, and Te, and no detectable impurity phases to an estimated sensitivity of 1%共three times the noise in the background of the x-ray patterns兲. Elemental analysis using inductively coupled plasma atomic emission spectroscopy共ICP-AES兲 confirmed that the phases produced had the compositions expected from the starting compositions.
For 关Bi0.75Te0.125Mn0.125兴Te, the temperature
dependen-cies of the zero field cooled 共ZFC兲 and field cooled 共FC兲 magnetization were measured on a quantum design magnetic property measurement system共MPMS兲 in an applied field of 100 Oe. The field dependence of the magnetization was mea-sured on a quantum design physical property measurement system共PPMS兲 fitted with an ACMS insert. The 2 K M共H兲 hysteresis loop was measured on the MPMS. The tempera-ture dependence of the sample resistivity was measured us-ing a standard four point method. For关Bi1−2xTexMnx兴Te and
关Bi1−xMnx兴Te the temperature dependencies of the ZFC mag-netic susceptibilities were measured on the PPMS in an ap-plied field of 10 kOe. M共H兲 curves at 5 K were measured on the same instrument. Low temperature ZFC and FC suscep-tibilities共2–30 K, H=100 Oe兲, and M共H兲 hysteresis curves at 2 K were collected on the MPMS.
CRYSTAL STRUCTURE
Profile analysis of the x-ray powder diffraction pattern 共Fig. 1兲 showed the single phase material of composition Mn0.33Bi2Te3to have the BiTe crystal structure共Fig.2兲 with
significantly smaller unit cell constants than are found for pure BiTe 共Table I兲. The crystal structure analysis showed that all the Mn and some of the Te occupy the Bi sites in BiTe. The formula of the compound is therefore best repre-sented as关Bi0.75Te0.125Mn0.125兴Te. The structural model with
Mn substituted in the Bi2 block and TeBi antisite defects in
the Bi2Te3 blocks resulted in the best Rietveld fits to the
diffraction data共TableI,2= 2.1兲. Models with Mn 共and Te Bi
antisites兲 in both the Bi2 and Bi2Te3 blocks were found to have significantly worse goodness of fit to the diffraction data. For example, a model with equal amounts of Mn and TeBion all Bi positions has2= 2.8. Structure refinements in
which Mn was omitted completely from the compound FIG. 1. Observed共crosses兲, calculated 共solid line兲, and
differ-ence PXD Rietveld profiles for关Bi0.75Te0.125Mn0.125兴Te. Reflection markers correspond to the Bragg positions.
yielded 2= 2.9, showing the sensitivity of the diffraction
data to the presence of the Mn. TableIpresents the structural parameters obtained and the agreement factors. These and the comparison of observed and calculated intensities shown in Fig.1indicate the high quality of the fit. The composition obtained by free refinement of the diffraction data is 关Bi0.75Te0.122共3兲Mn0.128共3兲兴Te, in excellent agreement with the
starting composition. This indicates that if any Mn is present in interstitial positions or secondary phases the amount would have to be minimal. The Mn atoms are preferentially located in the Bi2 block, which has stoichiometry
共Bi0.62Mn0.38兲2. This high proportion of Bi2block occupancy
explains why the earlier studies on TM doped Sb2Te3 and
Bi2Te3found that only a few atomic percent transition metal
substitution is possible:9–14there are no Sb
2or Bi2blocks in
those compounds. The amount of Mn on site 1 is exactly balanced by the amount of TeBiantisites on site 2共see Table
I兲. Interestingly, the TeBiantisite defects in the Bi2Te3layers
are all located on the Bi position closest to the Bi2 layer.
Deviations from 1:1 stoichiometry in BiTe, likely due to the presence of antisite defects of the type reported here, have been observed previously in mineral samples, where 关Bi0.58Te0.42兴Te and Bi关Te0.75Bi0.25兴 have been reported
with the BiTe structure.19 The bond distances in
关Bi0.75Te0.125Mn0.125兴Te are changed considerably from those
found in pure BiTe 共Table II兲, signaling a complex charge re-distribution upon Mn doping. The most obvious changes are the reduction of the Van der Waals gap between Te3-Te3 layers and the elongation of the共Bi/Te兲1-Te2 bonds.
Diffraction analysis of the 关Bi1−2xTexMnx兴Te series of samples, synthesized to conform to the Mn substitution and antisite defect structure found in the detailed structural analysis of 关Bi0.75Te0.125Mn0.125兴Te showed 0.033艋x
艋0.125 to be single phase and to have the BiTe structure. The PXD patterns are given in Fig.3. A systematic reduction in lattice constants with increasing x is found, confirming the presence of Mn substitution in a solid solution. For x = 0.133 and 0.167, a MnTe2impurity is found, therefore
de-fining the solubility limit in this compound series to be be-tween x = 0.125 and x = 0.133. Diffraction analysis of the 关Bi1−xMnx兴Te series of compounds, which were synthesized with no antisite defect chemical compensation, also found them to have the BiTe structure共Fig.3兲 but to have a much smaller Mn solubility range共up to x=0.067兲. For larger x, a MnTe impurity forms, defining the solubility limit in that case.
TABLE I. Refined atomic coordinates, temperature factors, and occupancies for Mn doped BiTe. The refined composition corresponds to关Mn0.128共3兲Bi0.75Te0.122共3兲兴Te.
Atom Pos. x y z Uiso共Å2兲 Occupancy
共Bi/Mn兲1 2d 2 / 3 1 / 3 0.4620共2兲 0.0130共6兲 0.62共1兲/0.38共1兲 共Bi/Te兲2 2d 1 / 3 2 / 3 0.2890共1兲 0.0130共6兲 0.63共1兲/0.37共1兲 Bi3 2c 0 0 0.1143共1兲 0.0130共6兲 1.00 Te1 2c 0 0 0.3759共2兲 0.0130共6兲 1.00 Te2 2d 2 / 3 1 / 3 0.1898共2兲 0.0130共6兲 1.00 Te3 2d 1 / 3 2 / 3 0.0454共2兲 0.0130共6兲 1.00
Space group P-3m1: a = 4.3783共1兲 Å, c=23.8107共8兲 Å. Residuals for the fit: 2= 2.1, wR
p= 11.4%, Rp = 8.8%, RF2= 9.0%.关Lattice constants for BiTe: a=4.423共2兲 Å, c=24.002共6兲 Å兴 共Ref.24兲.
TABLE II. Selected bond lengths 共Å兲 for 关Mn0.128共3兲Bi0.75Te0.122共3兲兴Te and corresponding bond lengths for BiTe共from Ref24兲.
Mn-BiTe BiTe 共Bi/Mn兲1-共Bi/Mn兲1 3.107共4兲 3.267共6兲 共Bi/Mn兲1-Te1 3.255共5兲 3.326共6兲 Te1-共Bi/Te兲2 3.268共4兲 3.166共9兲 共Bi/Te兲2-Te2 3.459共4兲 3.137共5兲 Te2-Bi3 3.102共3兲 3.355共6兲 Bi3-Te3 3.013共4兲 3.044共5兲
MAGNETIC AND ELECTRONIC PROPERTIES 共a兲 关Bi1−2xTexMnx兴Te: The inverse FC susceptibility for
x = 0.125 is given in the main panel of Fig. 4. The insets show the low temperature ZFC and FC susceptibility for x = 0.125 and the inverse FC susceptibilities, 1 /关共T兲-0兴 for
0.033艋x艋0.125. The temperature independent contribution 共0, given in Fig.4兲, due to core diamagnetism and
tempera-ture independent paramagnetic contributions, was obtained by fitting the susceptibility to共T兲=0+ C /共T-兲, where C is the Curie constant and the Weiss temperature. For x = 0.125, a Curie-Weiss fit in the 30 K艋T艋300 K interval 共solid line兲 giveseff= 4.90B/ Mn and= 8.6 K and0= 0.
The expected 共spin only兲 values for high-spin Mn3+ 共S=2兲
and Mn2+ 共S=5/2兲 are 4.9
B and 5.9B, respectively.
From the inset it can be seen that the Weiss temperature is close to zero for x艋0.067, while for x⬎0.067 positive val-ues are found, signaling the presence of ferromagnetic inter-actions. The occurrence of a ferromagnetic state for x = 0.100 and x = 0.125 is confirmed by Arrott plots关Figs.5共a兲 and5共b兲兴. Theory predicts that the 共high-field兲 isotherms of
M2 vs H / M are parallel lines for ferromagnets, and that the
isotherm at Tcpasses through zero.20The Curie temperature is close to 10 K for x = 0.125关Fig.5共a兲兴 and close to 5 K for
x = 0.100关Fig.5共b兲兴 as the intercepts of the linear fits to the M2 vs H / M plots at those temperatures are closest to 共0,0兲.
The insets in Figs.5共a兲and5共b兲show the as-measured M共H兲 FIG. 4. Magnetic susceptibilities for 关Bi1−2xTexMnx兴Te. The
main panel shows the temperature dependence of the inverse FC susceptibility for x = 0.125. The insets show the low temperature ZFC and FC susceptibility for x = 0.125 and inverse low temperature FC susceptibilities for 0.033艋x艋0.125.
isotherms. Both compositions show magnetic hysteresis at 2 K 关Fig. 5共c兲兴, characteristic of ferromagnetism. For x = 0.125, the coercive field Hc= 330 Oe and the remnant mag-netization Mr= 1.28B/ Mn. For x = 0.100, Hc= 79 Oe, and
Mr= 0.21B/ Mn. For x = 0.033 and x = 0.067 no hysteresis is
observed. The linear increase of the magnetization in high-fields共temperatures below Tc, insets in Fig.5兲 can be attrib-uted to magnetocrystalline anisotropy: whereas the easy-axis magnetization can saturate within accessible low field ranges, the magnetization along the hard axes usually in-creases linearly with field over the same low field range.20
This is consistent with the finite slope of the field dependent average magnetization as observed in our polycrystalline samples.
共b兲 关Bi1−xMnx兴Te: The temperature dependence of the in-verse ZFC susceptibilities, 1 /关共T兲-0兴 are shown in Fig.6,
and the field dependencies of the magnetization at 5 K are shown in the inset. The inverse susceptibilities almost over-lap. Curie-Weiss fitting共5艋T艋150 K兲 resulted in effective moments of 4.9B/ Mn for both x, while the Weiss
tempera-tures are small and negative关= −2共1兲 K兴. The effective mo-ments are close to that observed for关Bi0.75Te0.125Mn0.125兴Te.
The observed magnetizations at 5 K and 50 kOe are approxi-mately 2.5B/ Mn for both compositions.
A comparison of the effective moments, Weiss tempera-tures and magnetization at 5 K and 50 kOe for 关Bi1−2xTexMnx兴Te and 关Bi1−xMnx兴Te is given in Fig.7. The effective moment for关Bi1−2xTexMnx兴Te increases to what ap-pears to be an asymptotic value of 4.9B/ Mn. The same
value is found for both 关Bi1−xMnx兴Te compositions. The Weiss temperature is close to 0 K for x艋0.067 in both se-ries, while for x⬎0.067, is positive for关Bi1−2xTexMnx兴Te with a maximum of +8.6 K共x=0.125兲. The magnetization at 5 K and 50 kOe increases linearly with x and reaches a maximum of 3.2B/ Mn for x = 0.125. This is smaller than
expected for high-spin Mn3+ 共4
B兲 and Mn2+ 共5B兲. The
present experimental data do not allow for an unambiguous determination of the Mn valence state. The effective moment and magnetization共5 K, 50 kOe兲 are closer to the expected values for Mn3+ than for Mn2+. Specifically the effective
moment共4.9B/ Mn兲 is in very good agreement. However,
it must be noted that recent results on thin films of
Ga1−xMnxAs show a magnetization around 4 B/
Mn-4.5B/ Mn after correction for interstitial Mn defects.2In the
current case, the observed magnetization could also be re-duced from its expected value due to compensation from some fraction of the Mn, which as in the case of Ga1−xMnxAs may be antiferromagnetically coupled. Investigations into the importance of compensation by interstitial Mn and explana-tion of the doping dependence of the magnetic properties are for future studies. The main conclusion from this work is the observation of ferromagnetism in关Bi1−2xTexMnx兴Te.
The temperature dependence of the resistivity of 关Bi0.75Te0.125Mn0.125兴Te is given in Fig.8and is typical of a
degenerate semiconductor or poor metal. The weak tempera-ture dependence 共the residual resistivity ratio is 1.52兲 indi-cates charge carrier scattering is dominated by structural de-fects or impurities, consistent with the random doping of Mn in the共2兲 blocks and the presence of TeBiantisite defects in
the共5兲 blocks. The insets show the temperature dependencies of the Seebeck coefficient共S兲 and the thermal conductivity 共兲. The negative sign of S indicates that n-type conduction is dominant, and the magnitude is comparable to that ob-served for BiTe. 共SRT= −30V / K, on our samples兲. The
change of curvature around 20 K coincides with the maxi-mum in thermal conductivity and the minimaxi-mum in resistivity. The field dependence of the Hall resistivity of 关Bi0.75Te0.125Mn0.125兴Te is given in Fig. 9. The data reveals
the presence of an anomalous Hall effect, which exists to temperatures above Tc. In metals, ferromagnetism is invari-ably accompanied by the existence of a large anomalous Hall effect. The observed Hall resistivityxyis comprised of two contributions, viz.
FIG. 6. Temperature dependence of the inverse susceptibility for 关Bi1−xMnx兴Te. The inset shows the M共H兲 dependence up to 50 kOe.
xy= R0H + RsM , 共1兲 where R0and Rs are the ordinary and anomalous Hall coef-ficients, respectively, and M is the magnetization. The strongly nonlinear field profile ofxyis made up of the linear term R0H and the nonlinear term RsM that reflects the H dependence of M. In the present system, the anomalous term is strongly in evidence at 4.5 K, and is superposed on an
n-type H linear term. We have found that, above Tc, the anomalous term remains quite sizable 共e.g., see the 15 K data in Fig. 9兲. A detailed study of this will be reported elsewhere.21The interesting extension of the anomalous term
high above Tcis also observed in other ferromagnetic sys-tems including Ga1−xMnxAs.22 By separating the ordinary term R0in Eq. 共1兲, we have derived the carrier density n in
关Bi0.75Te0.125Mn0.125兴Te. Figure 9 shows that, over a broad
interval of T, n has a nearly constant value⬃7⫻1020cm−3.
This is two orders of magnitude higher than the value re-ported in Bi2Te3.23
CONCLUSIONS
The substitution of Mn in BiTe is demonstrated for the first time. Structural analysis for 关Bi0.75Te0.125Mn0.125兴Te
shows that Mn preferentially occupies sites in the Bi2blocks
and is accompanied by an equal amount of TeBiantisite
de-fects. These antisite defects greatly increase the solubility of Mn, as demonstrated by the relative phase stabilities of the 关Bi1−xMnx兴Te and 关Bi1−2xTexMnx兴Te series. This indicates that electronic considerations significantly influence the crys-tal chemistry of these systems. 关Bi1−xMnx兴Te shows little change in magnetic properties with x and remains paramag-netic down to 5 K. The magnetism in关Bi1−2xTexMnx兴Te on
the other hand shows a clear doping dependence, and, for x larger than 0.067 ferromagnetism is observed. From simple chemical arguments共Te has one more valence electron than Bi兲 the TeBiantisite defects in the Bi2Te3blocks are expected
to be single donors. The effect of Mn substitution in the Bi2 layers is harder to predict but it is likely that Mn acts as an acceptor and the TeBi antisite defects and MnBi partially
compensate each other, resulting in a greater Mn solubility. 关Bi0.75Te0.125Mn0.125兴Te has been studied in most detail
and has a Tcclose to 10 K. In this case, the composition of the Bi2block is approximately共Mn0.4Bi0.6兲2. Such large Mn concentrations in neutral hosts does not automatically result in ferromagnetism; as demonstrated by Zn1−xMnxTe and Cu1−xMnx, which are spin glasses. On the other hand, ferro-magnetism with Tcup to 170 K is observed in Ga1−xMnxAs. In the latter case, the introduction of Mn is accompanied by charge carrier doping and this appears vital for the occur-rence of ferromagnetism. The localization of Mn in the two-layer wide Bi blocks in BiTe, creating two-layers of relatively high Mn concentration, and the charge compensation due to the TeBi antisite defects, appear to be important factors in why Mn-doped BiTe becomes ferromagnetic at low tempera-tures. The fact that Mn-doped BiTe is a unique bulk system in which structural analysis is possible, showing the loca-tions of both the doped Mn and charge compensating defects, suggest that it is worthy of further study as a model for transition metal doping induced ferromagnetism in semicon-ductors provided single crystals can be grown.
ACKNOWLEDGMENTS
This research was supported in part by the MRSEC pro-gram of the National Science Foundation, and in part by the Air Force Research Laboratory.
FIG. 9. Field dependence of the Hall resistivity at selected tem-peratures. The inset shows the temperature dependence of the car-rier density determined from the ordinary Hall coefficient. FIG. 8. Temperature dependence of the electrical resistivity for
1S. A. Wolf, D. D. Awschalom, R. A. Buhrman, J. M. Daughton, S. von Molnar, M. L. Roukes, A. Y. Chtchelkanova, and D. M. Treger, Science 294, 1488共2001兲.
2T. Jungwirth, K. Y. Wang, J. Masek, K. W. Edmonds, J. Konig, J. Sinova, M. Polini, N. A. Goncharuk, A. H. MacDonald, M. Saw-icki, A. W. Rushforth, R. P. Campion, L. X. Zhao, C. T. Foxon, and B. L. Gallagher, Phys. Rev. B 72, 165204共2005兲. 3A. H. MacDonald, P. Schiffer, and N. Samarth, Nat. Mater. 4,
195共2005兲.
4T. Story, R. R. Galazka, R. B. Frankel, and P. A. Wolff, Phys. Rev. Lett. 56, 777共1986兲.
5A. Haury, A. Wasiela, A. Arnoult, J. Cibert, S. Tatarenko, T. Dietl, and Y. M. d’Aubigne, Phys. Rev. Lett. 79, 511共1997兲. 6D. Ferrand, J. Cibert, A. Wasiela, C. Bourgognon, S. Tatarenko,
G. Fishman, T. Andrearczyk, J. Jaroszynski, S. Kolesnik, T. Di-etl, B. Barbara, and D. Dufeu, Phys. Rev. B 63, 085201共2001兲. 7J. K. Furdyna, J. Appl. Phys. 64, R29共1988兲.
8P. Gibbs, T. M. Harders, and J. H. Smith, J. Phys. F: Met. Phys. 15, 213共1985兲.
9J. S. Dyck, P. Hajek, P. Losit’ak, and C. Uher, Phys. Rev. B 65, 115212共2002兲.
10J. S. Dyck, C. Drasar, P. Lost’ak, and C. Uher, Phys. Rev. B 71, 115214共2005兲.
11J. S. Dyck, P. Svanda, P. Lost’ak, J. Horak, W. Chen, and C. Uher,
J. Appl. Phys. 94, 7631共2003兲.
12V. A. Kulbachinskii, A. Y. Kaminskii, K. Kindo, Y. Narumi, K. Suga, P. Lostak, and P. Svanda, Physica B 311, 292共2002兲. 13J. Choi, S. Choi, Y. Park, H. M. Park, H. W. Lee, B. C. Woo, and
S. Cho, Phys. Status Solidi B 241, 1541共2004兲.
14J. Choi, H. W. Lee, B. S. Kim, S. Choi, J. Choi, J. H. Song, and S. L. Cho, J. Appl. Phys. 97, 10D324共2005兲.
15F. Hulliger, Structural Chemistry of Layer-Type Phases 共D. Re-idel Publishing Company, Dordrecht, 1976兲.
16H. Lind, S. Lidin, and U. Haussermann, Phys. Rev. B 72, 184101 共2005兲.
17E. Gaudin, S. Jobic, M. Evain, and R. Brec, Mater. Res. Bull. 30, 549共1995兲.
18A. C. Larson and R. B. Von Dreele共Los Alamos National Labo-ratory, Report LAUR 86-748, 2000兲.
19P. Bayliss, Am. Mineral. 76, 257共1991兲.
20B. Barbara, D. Gignoux, and C. Vettier, Lectures on Modern
Magnetism 共Science Press Beijing and Springer-Verlag Berlin
Heidelberg, 1988兲.
21M. Lee et al.共to be published兲. 22H. Ohno, Science 281, 951共1998兲.
23V. D. Das and N. Soundararajan, Phys. Rev. B 37, 4552共1988兲. 24K. Yamana, K. Kihara, and T. Matsumoto, Acta Crystallogr., Sect.
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